Torsion balance



March 30, 1937. E. ROUX ET AL TORSION BALANCE Filed July 26, 1952 4 sheets-sheet 1 March 30, 1937. E. ROUX ET AL TORSION BALANCE Filed July 26,- 1932 4 Sheets-Sheet 2 March 30, 1937. E. ROUX ET AL 2,075,625

TORSIONBALANCE Filed July 26, 1932 4 Sheefs-She'et s March 30, 1937.

E. ROUX ET AL TORSION BALANCE Filed July 26, 1932 4 Sheets-Sheet 4 r Patented Mar. 30, 1937 UNITED STATES TORSION BALANCE Erwin Roux, Berlin-Friedenau, and Hermann Imhof, Berlin-Steglitz, Germany, assignors to Askania- Werke Aktiengesellschaft,

Berlin- Friedenau, Germany, a corporation of Germany Application July 26, 1932, Serial N6. 624,776 In Germany July 29, 1931 8 Claims.

This invention relates to torsion balances and more particularly to Eotvos torsional balances.

The invention and its aims and objects will be clearly understood from the following description taken in connection with the accompanying drawings of the embodiments of the invention hereingiven for illustrative purposes, the true scope of the invention being more particularly pointed out in ,the appended claims.

In the drawings:

Fig. 1 is a front elevation of a torsion balance embodying one illustrative form of the invention, the protective casing being shown in section;

Fig. 2 is a top plan view of the embodiment shown in Fig. 1;

Fig. 3 is a vertical section on line 33 of Fig. 4;

Fig. 4 is a top plan sectional view of the embodiment of the invention shown in Fig. 1;

Fig. 5 is a longitudinal sectional view of a suspension housing on line 5-5 of Fig. 4;

Fig. 6 is a cross sectional view of a suspension housing on line 6-6 of Fig. 5 to illustrate more particularly the locking means for the balance beam;

Figs. 7 to 10 show diagrammatically the paths followed by the light rays in a preferred and particularly advantageous arrangement of the suspension mirror or prism;

.Fig. 11 is a vertical sectional elevation of another illustrative embodiment of the invention;

Fig. 12 is a top plan view of the embodiment shown in Fig. 11;

Figs. 13 and 14 show an illustrative path for recording light rays.

.comprises a hollow central body portion 2, the

median portion t of which is polygonal in cross section. Herein said median portion is hexagonal in cross section thus forming a hexagonal prism (Figs. 3 and 4) In this illustrative embodiment of the invention, the torsion balances each comprise a balance beam and a suspension therefor mounted in a separate housing 6', all of said housings being similar in construction (Figs. 3 and 5) Each suspension housing 6 comprises a median portion 8, preferably of prismatic shape having an upward extension in carrying the torsion head l2 from which is suspended the torsion. thread id for the balance beam IS. The balance beam I6 is secured to a support l8 suspended from the torsion thread [4. Said support [8 also carries the reflecting surface, herein preferably consisting of a prism 20, which serves for rendering visible the torsional oscillations of the balance beam l6 by means of reflected light rays. In accordance with the present invention the balance beam 16 hangs in an inclined position when at rest. This enables a straight or rectilinear balance beam to be used for the protection of which a simple cylinder or prismatic box or casing 22 can be employed. The suspension housings are thus characterized by the simple shape shown in Fig. 5.

The suspension housings 6, 22 may be secured to the median portion 4 in any suitable manner and by any suitable means, each suspension housing being herein secured to a lateral face of the prismatic median portion t by bolts or screws 26 extending into the wall of said face through eyes 26 carried by the suspension housing (Fig. 1). It will be apparent that any number of suspensions may be employed without departing from the spirit of the invention, the number of faces on the prism i being correspondingly multiplied.

The invention comprises means for locking the balance beam it in position when not in use. Any suitable means may be provided for this purpose, in accordance with the invention, said means herein conveniently comprising an extended member 28, U-shaped in cross section (Figs. 5 and 6). Said member is carried by a stud 3i! by which it is supported in an inclined position adjacent and parallel to the balance beam it. This stud is guided for vertical movement in a bore 32 provided in a boss Mprojecting downwardly from the suspension housing 8, and is secured against rotary movement in said bore by any suitable means, as by a pin and slot connection (not shown) for example. The stud 30 is provided with an axial bore 32 which is screwthreaded to receive a screw-threaded stud 3B having a knurled disk 38 secured thereto. By rotating the disk 38 the stud 36 which is held against vertical movement in the boss 35 by a collar Ml on said stud engaging an annular groove in said boss will raise said stud 30 and the member 28 will be moved substantially parallel to itself to clamp the balance beam t6 against the upper side 29 of the housing 6 to lock it against movement when not in use. Toprevent the balance beam from slipping downwardly said member 28 is provided at its lower end with an end wall 42 which overlaps the lower end of said balance beam.

Means are herein provided simultaneously to look a plurality of balance beams against movement when not in use or to release the same for operation. Said means herein illustratively comprises brackets 44 carried by the base portion 46 of the body of the apparatus, one of said brackets I being located below each of the bosses 34 ,each having journaled therein a short shaft 46a and carrying at its lower end a pinion 48. Each of said shafts 46a is in vertical alignment with the stud 36 of the corresponding suspension housing 6, and its upper end is provided with a squared recess 50 adapted to be engaged by the squared lower end 32a of the stud 36 (Fig. 3). The pinions 48 of which only one is shown in Fig. 3, mesh with a large gear 52, mounted for rotation upon said base of the apparatus and provided with a hand wheel 54 for rotating the same.

When the suspension housings 6 are placed in position in the apparatus the squared lower ends of the studs 36 engage the square recesses 56, so that by turning the wheel 54 all of the balance beams may be simultaneously locked when not in use or released simultaneously for operation.

The means for observing or recording the oscillations of the balance beam are provided within the prismatic portion 4 of the body portion of the apparatus (Fig. 3).

Each of the prismatic faces of said portion 4 is provided with a window 56 which, when the suspension housings are placed in position coincides with a window 58 provided in the rear wall of the median portion 8 of said housing. Flaps or any other suitable means (not shown) may be provided to close said windows when the apparatus is not in use to prevent the penetration of dust. Opposite each window there is provided within said portion 4 a reflecting surface, herein a right angle prism 60, by which the light rays reflected by the reflecting surface or prism 20 on the balance spindle are reflected upwardly in a substantially vertical direction. Within the upper portion 62 of the body of the apparatus a reflecting surface, herein a right angle prism 64, is provided opposite each of said prisms 60, the rays received from the latter being thus reflected by said prisms 64 in a lateral direction (Figs. 3 and 5). The prisms 64 will'preferably be in different vertical and horizontal planes in order that the light rays corresponding to the difi'erent suspensions may be observed through superposed eye pieces 66. Sources of light 68, of which one is shown in Fig. 4 are provided adjacent said eye pieces, the light rays from said sources of light being reflected by said prisms 84 through lenses 70, by which they are brought into parallelism, and are then reflected by said prisms 60 against the reflecting surface 20 on the balance beam by which they are again reflected back to prisms 60, lenses 10 and by prisms 65 back to the eye pieces 66.

In accordance with the present invention the reflecting means 20 on the obliquely suspended balancebeam I6 is positioned and arranged in v the particular manner illustrated in Figs. 7 to 10 for the following reasons. An obliquely suspended beam inaddition to executing the oscillations about the torsion thread, which it is desired to measure, also executes oscillations of short frequency about the main inertia axis, that is to say about that axis with relation to which the balance beam possesses its lowest polar moment of inertia. If therefore the reflecting surface on said beam were positioned parallel to the torsion thread, as is usual, said surface would be inclined at an acute angle to the main inertia axis indicated in Figs. 7 and 8 by broken lines, and said reflecting surface would therefore, when the balance beam oscillates about said main inertia axis, execute movements that would divert the light ray. These oscillations manifest them- -larly bent ends of a bent balance beam exert a strong damping action upon oscillations about the main inertia axis; so that such oscillations, particularly where the balance is of relatively large dimensions, are not noticeable to such an injurious degree. In the case of torsion balances provided with straight obliquely suspended balance beams, there is no such damping action, so that the practically undamped oscillations about the main inertia axis manifest themselves to such an injurious extent that a reading, or a recording that could be read, cannot be obtained.

These disadvantages are eliminated in the simplest manner by the present invention by a special arrangement of the reflecting surfaces on the balance beam or other means for diverting the light rays which are to serve for reading or registering due to which special arrangement the torsional or rotary oscillations of the beam about its main inertia axis have no effect upon the reflected light ray to be used for reading or for registration. If a simple mirror be used for indicating the torsional oscillations, said mirror will be positioned upon the balance beam in such manner that its reflecting surface shall be subments heretofore used. Instead of using a single reflecting surface two reflecting surfaces inclined at an angle relative to each other may be used. In the latter case the two reflecting surfaces will be so positioned that the line of intersection of said two surfaces shall be parallel to the main inertia axis. Preferably the inner surface of a triangular prism will be used as a reflecting surface, as illustrated in Fig. 5. The arrangement of two reflecting surfaces has the advantage that the entire system may be so arranged that the reflected beam or ray shall be directed practically horizontally, which permits the structure to be greatly simplified as compared to the arrangement wherein only a single reflecting surface at right angles to the main inertia axis is used, as then the reflected ray naturally is direct- .ed substantially in the direction of the main inertia axis. The main'inertia axis itself, that is to say the position to be given to the mirror or other reflecting surface, is very readily determined because, in the case of an inclined straight balance beam the main inertia axis extends'practically parallel to the geometrical axis of the beam, while in the case of the once or twice right angularly bentbeams heretofore generally used, the main inertia axis can be considered as running practically through the center of gravity of the weights, as the other parts of the balance beam are made of the lightest possible material so that their weight-as compared to the mass of the Eotvos weights themselves is not worth considering.

The nature and mode of operation of this arrangement will be apparent from Figures 7 to 10 in which Fig. 7 shows a straight obliquely suspended beam having a single mirror. Fig. 8 shows a similar beam similarly suspended having a prism as in Fig. 5, while Figs. 9 and 10 show the paths followed by the light rays where two reflecting surfaces are used.

Referring to Fig. '7, the mirror 12 is mounted at right angles to the main inertia axis I4 of the balance beam I6. When the beam oscillates 10 about the main inertia axis H, the axis of incidence or normal line of the mirror undergoes no deviation, so that the light ray to be used for observation or registration also undergoes no deviation. In the modification shown in Fig. 8,

15 a triangular prism is so positioned at the point of suspension I8 of the balance beam I6 that one prism edge 16 is parallel to the main inertia axis I4, which in this case difiers only slightly from the geometrical axis of the balance beam.

20 Referring to Fig. 9, a light ray entering the bottom surface I8 of the prism strikes the lateral surface 80 from which it is reflected against the other lateral surface 82 andis reflected by the latter out through the bottom surface again. If

this prism be turned about the edge I6 there will be no deviation of the reflected light ray emerging from the prism. As will be apparent from a simple geometrical consideration of the matter the twice reflectedlight ray emerging from the bottom surface of the prism will rotate through exactly the same angle through which the incident ray is turned. It is particularly advantageous to use a right-angled isosceles prism because in such a prism the light ray twice reflected by the two side surfaces of the right angle leaves the prism parallel to the incident or entering ray. The path followed by the ray in the case of rotation through a small angle is shown in Fig. 10.

If on the other hand the prism be turned about an edge that is perpendicular to the edge 16, the reflected light ray leaving the prism through its bottom surface It will be diverted, as diagrammatically shown in Fig. 10.

. As a rotation about the torsion thread I4,

which is inclined relative to the prism edge I6, may be considered as made up of two rotations, one about an axis parallel to the edge "I6, the other about an axis perpendicular to the edge I6,- it results that in the described arrangement of the prism 20, movement of the prism produced by oscillationsof the balance beam about its- Adjustment of the balance for recording purposes 7 teries for the incandescent bulbs which herein constitute the sources of light.

In the illustrative embodiment of the inven tion only three light ray paths are shown for three suspensions. Each lateral surface of the '75 prism shaped middle portion l of the apparation can be given any other number of lateral I surfaces, thus making possible other combinations which may be of advantage in the case of particular problems.

Before beginning to make measurements with a torsion balance it must be carefully adjusted, particularly as regards the perpendicular and the azimuth. -The torsion balance embodying the present invention enables a removable ad justment table to be used. For this purpose there may be provided upon the upper portion of the median body 4 and preferably upon extensions 84, B6 and 68 suitable means, herein three studs 92 (Figs. 1 and 2) upon which an adjustment table 64 having three feet 96 may be readily and securely positioned. Said table itself will preferably be provided with two tubular levels 98, 98 disposed at right angles to each other, and a compass I66. This arrangement is particularly advantageous because it enables the adjustment table to be positioned on the torsion balance even if the latter be enclosed in a protective housing I62 made out of artificial resin or some other compressed material. All that is required is to make the necessary bores in the protective housing to receive the studs 92.

The means (Fig. 3) to enable the torsion balance to .be rotated from one observation azimuth into another may be of any suitable construction, for example the base portion 46 of the body of the apparatus may be mounted to turn on ball bearings IM about a vertical shaft I66 rising centrally from horizontal base plate I08.

In the second embodiment of the invention illustrated in Figs. 11 to. 13, only two suspensions are provided, although it will be apparent to those skilled in the art that three, four orv more could be used. This embodiment of the invention differs essentially from the other in'that th light rays serving for the measurement of the oscillations are differently guided, that is to say, follow a different path, so that the execution is different from an optical point of view. The outer construction of the median casing is the same with the exception that the extensions 64,

86 and 88 at the top are omitted, and that the.

top plate I I6 is arranged to receive a light sensitive plate holder, guides H2 being provided for this purpose between which the holder is slid into position with the light sensitive surface facinglownward. In an opening II I, provided in the lateral wall of the upper portion, there is provided an incandescent bulb II6 from which the light required to make the oscillations of the balance beam visible is projected, preferably through a condenser lens (not shown). A prism II8 reflects the light vertically downward where it strikes a, mirror I20 which reflects the light upwardly against an inclined mirror I22. From this mirror I22 the ray of light is reflected by a further prism I24 to the reflecting surface of prism 26 upon the suspension; said prism 2t being mounted upon the balance beam with its edge parallel to the latter, as in the first em bodiment described. From the suspension prism 20 the'light falls upon a mirror I26 mounted within the part 8 of the housing. From the mirror I26 the ray of light is reflected back to the suspension prism 20 and thence to said prism I 24, and thence to said inclined mirror I22 and to a mirror I28. The latter reflects the ray of light in the direction I30, so that it falls upon the light sensitive layer as shown at I30a, Fig. 13, 5 if such be used, and the oscillations of the balance beam are recorded in the usual manner upon said light sensitive layer or surface.

Figs. 13 and 14 show clearly the path followed by the ray of light, Fig. 13 showing a side view.

of the optical instrumentalities and the path followed by the light ray looking vertically downward on the suspension housing, while Fig. 14 shows the optical instrumentalities and the path followed by the ray of light as seen from above.

5 In Fig. 14 the upper prism H8 and the lower mirrors IN and I28 have been omitted for the sake of clearness.

In order that this embodiment of the torsion balance may also be used for visual readings the mirror I28 may be journaled in two brackets I32,

only one of which is visible in Fig. 11. Upon the journal axis there is secured a lever I34-for.

adjusting the mirror about this axis. The lever I34 may be so arranged that its free end can be thrown into and out of mesh with a worm I36 provided upon an extension I33 of the shaft MB. When disengaged from said worm the end of said lever will be placed in a rest not shown. In this second position of the mirror I22 the ray of light, after being twice reflected to the suspension prism 20 will be diverted by the mirror I28 into the position I42 in which it strikes a second prism I which reflects it horizontally to an opening I 46 in which an eye piece may be provided for reading the deviations.

In the illustrative path followed by the ray of light the latter is twice reflected to the suspension prism 20. This has the advantage that the reflected ray of light instead of being reflected 40 through twice the angle as heretofore, is reflected through four times the angle through which the prism and hence the balance beam swings. In thisway the oscillation is made visible or recorded on twice as'large a scale as has heretofore been possible. By the use of similar means a. three, four or more times as great a reflection to the suspension mirror or prism could be secured.

The reflection of the ray of light from above '50 downwardly to the suspension prism and back again downwardly has the advantage of materially lengthening the path travelled by the ray of light, thereby increasing the amplitude of the oscillations observed or registered-andcorrespondingly increasing the accuracy. 7

The worm I36 with which the lever I34 may be caused to mesh as above set forth is important for the following reason. A measuring series made by a torsion balance, consists as is well 0 known of measurements in different observation azimuths. 'Where two suspensions are used the observations are usually in three azimuths diifer- 75 from the responsibility of-adjusting the mirrorafter the measurements in one azimuth have been accomplished and thus avoids any danger that by forgetting to adjust the mirror an observation series may be rendered useless. The construction shown using the worm I 36 and lever I34 has the great advantage of extreme simplicity of construction with a minimum of parts as comparedto other constructions heretofore used'to accomplish the same end.

Besides the advantages pointed out in the course of the specification the provision of a separate housing for each suspension, said housings being readily exchangeable and supported laterally upon a central body containing the optical instruments and the viewing or reading and recording means is particularly advantageous, because apart from the fact that such a construction is extremely favorable from the manufacturing viewpoint since it permits construction of the balance out of a number of parts that are all alike, there is the further advantage that this novel torsion balance permits the suspensions to be readily changed at any time as will sometimes become necessary in the case of breakage of the torsion thread or similar reasons when fresh one containing a new thread. Furthermore the prismatic construction of the housing enables one and the same torsion balance to be used with different numbers of suspensions. If the central body is in the form of a hexagonal prism, for example, the balance may be used with two, three, four or six suspensions; it is only necessary to have on hand a corresponding number of replacement housing parts.

We are aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and we therefore desire the present embodiments to be considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the above description to indicate the scope of the invention.

We claim:

l. Torsion balance apparatus comprising, in combination, a support housing having viewing means at its upper portion'and transparent portions spaced about its side walls; means on the exterior of said housing adjacent each of said transparent portions for detachably mounting a torsion balance thereon as a unit; and means within said housing for receiving beams of light from each of said units reflected through said transparent portions and projecting said beams upon said viewing means.

2. Torsion balance apparatus comprising, in combination, a support housing of prismatic shape having viewing means at its upper portion and transparent portions in its plane side walls; means for detachably mounting a torsion balance as a unit on the exterior plane side walls of said housing adjacenteach of said transparent portions, said unit having means to mate with said mounting means and an opening to register with the transparent portion of said housing; and means within said housing for receiving beams of light from each of said units reflected through said openings and projecting said beams upon said viewing means.

3. Torsion balance apparatus comprising, in combination, a support housing having viewing means at its upper portion andtransparent portions spaced about itsside walls; a plurality of torsion balances, each forming an interchangeable unit comprising a balance beam, a housing therefor and balance beam suspension; means on the exterior of said support housing adjacent each of said transparent portions for detachably mounting a torsion balance thereon as a unit; and means within said support housing for receiving beams of light from each of said units reflected through said transparent portions and projecting said beams upon said viewing means.

4. Torsion balance apparatus comprising, in combination, a supporthousing having viewing means at its upper portion and transparent portions spaced about its side walls; means on the exterior of said housing adjacent each of said transparent portions for detachably mounting a torsion balance thereon as a unit; means within said housing for receiving beams of light from each of said units reflected through said transparent portions and projecting said beams upon said viewing means; and means associated with said units and operable simultaneously to lock said torsion balances against movement.

5. Torsion balance apparatus comprising, in combination, a support housing of prismatic shape having viewing means at'its upper portion and transparent portions in, its plane side walls; a plurality of torsion balances, each forming an interchangeable unit comprising an oblique balance beam, a housing therefor and balance beam suspension; means on the exterior of said support housing adjacent each of said trans parent portions for detachably mounting one of said torsion balances on each plane side wall as a unit; and means within said-support housing for receiving beams of light from each of said units reflected through said transparent portions and projecting said beams upon said viewing means.

.6. Torsion balance apparatus comprising, in combination, a support housing of prismatic shape having viewing means at its upper portion and transparent portions in its plane side walls; means on the exterior plane side walls of said housing adjacent each of said transparent portions for detachably mounting an inclined torsion balance thereon as aunit, said torsion balance carrying a reflecting surface in a plane at right angles to the main inertia axis of said torsion balance; and means within said housing for receiving beams of light from said reflecting surfaces of said units reflected through said transparent portions and projecting said beams upon said viewing means.

7. Torsion balance apparatus comprising, in combination, a support housing of prismatic shape having viewing means at its upper portion, and transparent portions in its plane side walls; means on the exterior of said housing adjacent each of said transparent portions for detachably mounting an inclined torsion balance on a plane wall thereof asa unit, said torsion balance carrying two reflecting surfaces in planes that intersect along a line parallel to the main inertia of said torsion balance;

and means within said housing for receiving beams of light from said reflecting surfaces of said units reflected through said transparent portions and projecting said beams upon said viewing means.

8. Torsion balance apparatus comprising, in combination, a support housing of prismatic shape having viewing means at its upper portion and transparent portions in its plane side walls; means on the exterior of said housing adjacent said transparent portions for detachably mounting an inclined torsion balance on a plane side wall thereof as a unit, said torsion balance carrying a right-angle isosceles prism, the line of intersection of the surfaces forming the rectangle of said prism being parallel to the main inertia axis of said torsion balance.

ERWIN ROUX. HERMANN IMHOF. 

